Novel chromium plating compositions

ABSTRACT

THIS INVENTION RELATES TO NOVEL COMPOSITION AND TO A PROCESS FOR ELECTROPLATING CHROMIUM PLATE INTO A BASIS METAL WHICH COMPRISES PASSING CURRENT FROM AN ANODE TO A CATHODE AT LEAST A PORTION OF WHICH CONTAINS A CONDUCTIVE METAL LAYER THROUGH AN AQUEOUS ACIDIC CHROMIUM PLATING SOLUTION CONTAINING: (1) AT LEAST ONE CHROMIUM COMPOUND PROVIDING HEXAVALENT CHROMIUM IONS FOR ELECTROPLATING CHROMIUM; AT LEAST ONE CATALYST SELECTED FROM THE GROUP COMPRISING SULFATE IONS, COMPLEX FLUORIDE IONS AND FLUORIDE IONS; (2) AT LEAST ONE MEMBER OF THE GROUP CONSISTING OF SULFOACETATE AND SULFOACETIC ACID, ISETHINATE AND ISETHIONIC ACID, AND (3) AT LEAST ONE SOLUBLE COMPOUND CONTAINING SELENIUM; FOR A TIME SUFFICIENT TO DEPOSIT A CHROMIUM ELECTROPLATE HAVING A THICKNESS OF AT LEAST 1X10**4 MILLIMETER.

United States Patent 3,804,728 NOVEL CHROMIUM PLATING COMPOSITIONS Hyman Chessin, Birmingham, Mich., and Maurice Philip Best, Streetly, England, assignor to M 8: T Chemicals, Inc., Greenwich, Conn.

No Drawing. Continuation-impart of application Ser. No. 154,703, June 18, 1971. This application June 12, 1972, Ser. No. 262,151

Int. Cl. C23b /06 US. Cl. 204-51 12 Claims ABSTRACT OF THE DISCLOSURE This invention relates to novel compositions and to a process for electroplating chromium plate onto a basis metal which comprises passing current from an anode to a cathode at least a portion of which contains a conductive metal layer through an aqueous acidic chromium plating solution containing:

(1) at least one chromium compound providing hexavalent chromium ions for electroplating chromium; at least one catalyst selected from the group comprising sulfate ions, complex fluoride ions and fluoride ions;

(2) at least one member of the group consisting of sulfoacetate and sulfoacetic acid, isethionate and isethionic acid, and l (3) at least one soluble compound containing selenium;

for a time sufficient to deposit a chromium electroplate having a thickness of at least 1X millimeter.

This application is a continuation-in-part of US. patent application Ser. No. 154,703, filed June 18, 1971.

This invention relates to a novel process for the electrodeposition of chromium and to the novel chromium deposits formed thereby.

An object of this invention is to provide a process for electrodepositing Ibright decorative chromium plate.

An object of this invention is to provide a process for electrodepositing bright decorative microcracked chromium over a very broad current density range in a very short time interval.

Another object of this invention is to obtain microcracking in an intermediate current density region.

Other objects of the invention will be apparent to those skilled in the art upon inspection of the following detailed description of the invention.

This invention relates to novel compositions and to a process for electroplating decorative chromium plate onto a basis metal which comprises passing current from an anode to a cathode at least a portion of which contains a conductive metal layer through an aqueous acidic chromium plating solution containing:

(1) At least one chromium compound providing hexavalent chromium ions for electroplating chromium; at least one catalyst selected from the group comprising fiuoride ions, complex fluoride ions and sulfate ions;

(2) At least one member of the group consisting of sulfoacetate and sulfoacetic acid, isethionate and isethionic acid; and

(3) At least one soluble compound containing selenium.

The chromium electroplating bath compositions of the invention contain about 100-600 grams per liter of chromic acid (expressed as CrO and preferably about 100- 200 grams per liter of chromic acid.

The plate produced by the novel process of this invention is highly satisfactory with respect to its unusually bright decorative appearance.

ice

. According to another of its aspects this invention is a method of forming a surface upon a substrate comprising a duplex plating of two disparate kinds of chromium comprising:

(1) electrodepositing an-ordinary chromium first layer and then (2) electrodepositing on said first layer of chromium a layer of microcrack chromium having at least 40 cracks per centimeter comprising maintaining an aqueous chromium plating bath containing chromic acid, sulfate ions, active fluoride ions, and

(3) at least one soluble compound containing selenium,

and

at least one member of the group consisting of:

(a) sulfoacetate (b) sulfoacetic acid (0) isethionate (d) isethionic acid While sulfoacetic acid itself imparts homogeneous microcracking, isethionates, such as sodium isethionate, are readily oxidized to sulfoacetic acid by the chromic acid plating bath and also elfect enhanced microcracking of chromium. Thus, it has been found that sulfoacetic acid has been found to produce a very different structure in heavy chromium deposits. The amount of sulfoacetic acid added to the chromic acid bath should be between 1 gram per liter and 10 grams per liter, preferably about 3 grams per liter.

The aqueous chromium plating baths of this invention contain selenium in soluble form. Soluble selenium may be introduced into the bath by dissolving therein a compound containing selenium which is soluble in the bath. Operable selenium-containing compounds include selenic acid and salts thereof, such as sodium selenate, ammonium selenate, potassium selenate, selenous acid and salts thereof, such as sodium selenite, potassium selenite; lower alkyl esters of selenic acid and selenous acid such as dimethyl selenate, diethyl selenate, di-n-propyl selenate, di-sec-butyl selenate, dimethyl selenite, diethyl selenite, diisopropyl selenite, di-n-butyl selenite, etc. Other compounds capable of contributing selenium in soluble form may also be employed.

Typcally, the selenium is present in the bath in the amout of 5X10" mole per liter Se and preferably 0.35 10 -10 10- mole per liter Se. The most preferred form of soluble selenium is selenate. Expressed as concentration of selenate, 560 the operable range is 0.5 milligram per liter to 15.0 milligrams per liter. The baths containing selenium, preferably selenate, within the noted ranges produce an exceptionally dense, fine microcrack pattern on cathodes plated even at intermediate current densities in remarkably short plating time according to the process of this invention.

The most highly preferred aqueous chromium plating baths may contain chromic acid, active fluoride preferably fluosilicate, sulfate, and selenium, preferably selenate.

In accordance with certain embodiments of this invention, the aqueous chromium plating bath may contain:

Highly Component Typical Preferred preferred Sulfate ions may be added to the chromium electroplating bath in the form of suitable sulfate compounds lithium sulfate (Li SO ammonium-sulfate calcium sulfate (CaSO etc.

The chromium electroplating process uses temperatures of 30-70 C. with a chromic acid bath containing 100-600 grams per liter of chromic acid (as CrO The ratio of chromic acid to sulfate ion (CrO :SO should be maintained at 50-550z1, typically 150-30021 and preferably about 200:1.

The aqueous chromium plating bath contains active fluoride. Active fluoride is fluoride ion in the form exhibiting catalytic activity in the bath. Active fluoride may be in the form of simple fluoride, F, or complex fluoride. Where complex fluorides are employed, one mole of complex fluoride may be considered equivalent to one mole of simple fluoride ion, i.e., both contribute approximately one mole of active fluoride to the bath. Typcially, the active flouride may be selected from the group consisting of fluoride (1 and complex fluorides including fluosilicate or silicofluoride (SiF fluoborate (BF4 fluoaluminate (AIF fluophosphate (PF fluozirconate (ZrF and fluotinate (TiF Fluosilicate may be the most preferred active fluoride.

The active fluoride may typically be present in the aqueous chromium plating bath in the amount of about 0.005-0.l5 mole per liter. Preferably, 0.01-0.05 mole per liter of active fluoride may be present. The active fluoride may be introduced into the bath by dissolving therein a salt or an acid of the active fluoride. Preferably, an alkali metal salt may be employed. Examples of suitable sources of active fluoride include sodium fluoride, potassium silicofluoride, fluoboric acid, sodium fluoalua minate, potassium fluophosphate, sodium bifluoride, potassium bifluoride, sodium fluotitanate, sodium fluozirconate, ammonium fluosilicate, and lithium fluosilicate.

Preferably, the aqueous chromium plating bath also contains sulfate ion, typically in the amount of about 0.2-5.0 grams per liter and preferably 0.3-4.0 grams per liter, say 1-3 grams per liter. The presence of sulfate ion improves the microcrack effect and the appearance of the chromium deposit and lowers plating time. The sulfate ion may be provided by dissolving in the bath sulfuric acid or a salt thereof having suflicient solubility to produce the desired concentration. Suitable sources of sulfate ion include sulfuric acid, sodium sulfate, potassium sulfate, magnesium sulfate, strontium sulfate, calcium sulfate, etc. The bath may contain common ion salts, e.g. potassium, strontium, calcium, lanthanum, praseodymium, neodymium, samarium, gadolinium, yttrium and didymium salts or mixtures thereof to limit the solubility of the catalyst ions to a desirable value in a self-regulating system.

Potassium ions may be added to the bath in the form of salts such as potassium fluosilicate, potassium dichromate, potassium carbonate, etc. When potassium ions are used in combination with fluosilicate ions, the chromium plating bath composition (containing 100-600 grams per liter CrO may be saturated with K SiF Such saturation is provided to obtain self-regulation of the catalyst content of the bath. Typically, from about 2 grams per liter to about 6 grams per liter or more of K SiF may be added to the chromium plating solution containing 100- 600 grams per liter of CrO to form a chromic acid solution which contains an excess of undissolved potassium fluosilicate (K SiF Potassium in the form of other soluble salts may be added to obtain suppression of the catalyst ion as taught by US. Pat. No. 2,640,022 which issued on May 26, 1953 upon the application of Stareck.

Rare earth ions or mixtures of rare earth ions may be added to the bath in the form of salts such as lanthanum or didymium salts or complex salts. Where these ions are used in combination with fluoride or complex fluorides the chromium bath may be saturated with the rare earth salt: Typically from about 1 to 10' grams per liter or more of the rare earth salt (including mixtures) may be added to the chromium plating solution containing -600 grams per liter of CrO to form a chromic acid solution which contains an excess of undissolved rare earth fluorides or complex fluoride. The following examples are submitted for the purpose of illustration only and are not to be construed as limiting the scope of the inventionin any way.

EXAMPLE 1 A 550-milliliter Hull Cell was used with an ordinary bath containing 200 grams per liter of chromic acid, 2.0 grams per liter of sulfate, 3.0 grams per liter of sulfoacetic acid, and 3 milligrams per liter of selenate to plate brass Hull Cell panels which had been bright nickel plated at 10 amperes for 10 minutes. After nickel plating the panels were given a water rinse, acid dip (10% sulfuric acid) and another water rinse. The panels were then placed in a slotted Hull Cell in a polyvinyl chloride tank and plated at 8 amperes for 6 minutes. The effect of adding 3 grams per liter of sulfoacetic 'acid and 3.0 milligrams per liter of selenate to this ordinary bath was that of enhanced microcracking in a reduced period of time.

EXAMPLE 2 (CONTROL) The process of Example 1 was followed except that all selenate was omitted. A total plating time of 8 minutes was required to obtain an acceptable deposit as compared with 6 minutes when selenate was included in the bath.

EXAMPLE 3 The process of Example 1 was again followed except that 4 milligrams per liter of selenate was employed. Again, in only 6 minutes, an acceptable deposit of microcracked chromium was obtained.

Thus, it is shown that the addition of as little as 3 or 4 milligrams per liter of selenate to the plating bath results in much shorter plating times as well as obtaining microcracking in intermediate current density ranges.

EXAMPLE 4 A SOO-milliliter Hull Cell was used with an all soluble salt bath of the following composition:

Component: Concentration Chromic acid (CrO g./l Sulfate (80 g./l 0.875 Fluosilicate (SiF g./l 0.375 Selenate (SeOf) mg./l 3.0

3 grams per liter of sulfoacetic acid were added to the bath to plate brass Hull Cell panels which had been nickel plated at 10 amperes for 10 minutes. After nickel plating the panels were given a water rinse, acid dip (10% sulfuric acid) and another water rinse. The panels were then placed in a slotted Hull Cell in a polyvinyl chloride tank and plated at 8 amperes for 6 minutes. The eifect'of adding 3.0 mg./l. of selenate and 3 grams per liter of sulfoacetic acid to this bath was that of enhanced microcracking in. the intermediate current density range in a demonstrably shorter time since when selenate was omitted a total of 8 minutes plating time was required to obtain an acceptable deposit.

EXAMPLE 5 Hull Cell panels were also plated using the following chromium plating bath composition:

Component: Concentration, g./l. Chromic acid (C'rO 175 Sulfate (S05) 0.58 Fluoride (F-) 0.30

With the addition of 6 grams per liter of sulfoacetic acid and 5 ml./l. of selenate using the same procedure as in Example 1, except that the plating time was. 5 min again enhanced microcracking was attained, substantiating that the microcracked chromium of this invention was attained in intermediate current density ranges in shorter plating time since omission of selenate resulted in a plating time of 8 minutes.

Although this invention has been illustrated by reference to specific embodiments, modifications thereof which are clearly within the scope of the invention will be apparent to those skilled in the art.

What is claimed is:

1. A process for electroplating decorative microcracked chromium plate onto a basis metal which comprises passing current from an anode to a cathode at least a portion of which contains a conductive metal layer through an aqueous acidic chromium plating solution containing:

(1) at least one chromium compound providing hexavalent chromium ions in an amount to provide a concentration of from 100 grams per liter to 600 grams per liter for electroplating chromium; at least one catalyst selected from compounds providing sulfate ions in a concentration of from 0.2 gram per liter to 5 grams per liter, complex fluoride ions and fluoride ions in a concentration of from 0.005 mole per liter to 0.15 mole per liter;

(2) at least one member of the group consisting of sulfoacetate and sulfoacetic acid, isethionate and isethionic acid providing sulfoacetic acid in a concentration of from 1 gram per liter to grams per liter; and

(3) at least one soluble compound containing selenium in an amount to provide a concentration of selenium of from 0.35 x10" moles per liter to 10x10" moles per liter;

for a time sufiicient to deposit a chromium electroplate having a thickness of at least 1X10- millimeter.

2. The process of claim 1 wherein said process is one for electrodepositing a bright decorative chromium plate and said isethionate is sodium isethionate.

3. A process for electroplating chromium plate onto a basis metal as claimed in claim 1 wherein the electroplating process is carried out at 30-70 C.

4. A process for electroplating chromium plate onto a basis metal as claimed in claim 1 wherein the aqueous acidic chromium plating solution contains about 100- 600 grams per liter of chromic acid and is saturated with a salt at 30-70 C. selected from those of the group consisting of salts of potassium, strontium, calcium, lanthanum, praseodymium, neodymium, samarium, gadolinium, yttrium and mixtures thereof.

5. A process for electroplating chromium plate onto a basis metal as claimed in claim 1 wherein the aqueous acidic chromium plating solution contains about 100-600 grams per liter of chromic acid, about 3 grams per liter of at least one member of the group consisting of sulfoacetate and sulfoacetic acid, isethionate and isethionic acid and 2 milligrams per liter to 10 milligrams per liter of selenate.

6. A process for electroplating chromium plate onto a basis metal as claimed in claim 1 wherein the aqueous acidic chromium plating solution contains about 200-350 grams per liter of chromic acid, about 3 grams per liter of at least one member of the group consisting of sulfoacetate and sulfoacetatic acid, isethionate and isethionic acid and 2 to 10 milligrams per liter of selenate.

7. A process for electroplating chromium plate onto a basis metal as claimed in claim 1 wherein the aqueous acidic chromium plating solution contains about 200-400 grams per liter of chromic acid, about 1-4 grams per liter of a salt selected from those of the group consisting of salts of potassium, strontium, calcium, lanthanum, praseodymium, neodymium, samarium, gadolinium, yttrium and mixtures thereof, and wherein the chromic acid to sulfate ion ratio is -550: 1.

8. A bath composition for electroplating chromium plate onto a basis metal which comprises:

(1) an amount of at least one chromium compound to provide a concentration of from 100 grams per liter to 600 grams per liter hexavalent chromium ions in an aqueous acidic chromium plating solution media, an amount of a compound to provide sulfate ions as catalyst, in a concentration of from 0.2 gram per liter to 5 grams per liter in an aqueous acidic chromium plating solution;

(2) an amount of at least one member of the group consisting of sulfoacetate and sulfoacetic acid, isethionate and isethionic acid, providing sulfoacetic acid in a concentration of from 1 gram per liter to 10 grams per liter in an aqueous acidic chromium plating solution; and

(3) an amount of at least one soluble compound containing selenium, in an amount to provide a concentration of selenium from 0.35 10- moles per liter to 10x10" moles per liter.

9. A composition for electroplating chromium plate onto a basis metal as claimed in claim 8 wherein the concentration of chromic acid is about 200-350 grams per liter and the composition for electroplating is saturated with a salt at 30-70 C. selected from those of salts of the group consisting of potassium, strontium, calcium, lanthanum, praseodymium, neodymium, samarium, gadolinium, yttrium and mixtures thereof.

10. A composition for electroplating bright decorative chromium plate onto a basis metal as claimed in claim 8 wherein the concentration of chromic acid is about 200- 350 grams per liter and the composition for electroplating contains about 3 grams per liter of at least one member of the group consisting of sulfoacetate and sulfoacetic acid, isethionate, and isethionic acid and about 2 milligrams per liter to 10 milligrams per liter of selenate.

11. A composition for electroplating chromium plate onto a basis metal as claimed in claim 8 wherein the concentration of chromic acid is 200-350 grams per liter and the composition for electroplating contains 1-4 grams per liter of a salt selected from those consisting of the group of salts potassium, strontium, calcium, lanthanum, praseodymium neodymium, samarium, gadolinium, yttrium and mixtures thereof.

12. A composition for electroplating chromium plate onto a basis metal as claimed in claim 8 wherein the concentration of chromic acid is about 200-400 grams per liter, the chromic acid to sulfate ion ratio is 50-550:1, and the composition for electroplating contains about 3 grams per liter of at least one member of the group consisting of sulfoacetate and sulfoacetic acid, isethionate and isethionic acid and at least 0.5 milligram per liter of selenate.

References Cited UNITED STATES PATENTS 2,640,022 5/ 1953 Stareck 204-51 2,800,443 7/ 1957 Stareck et al 204-51 3,340,165 9/ 1967 Chessin 204-51 3,408,272 10/ 1968 Such et al. 204-51 3,563,864 2/1971 Du Rose et al. 204-51 X 3,661,733 5/ 1972 Roggendorf 204-51 GERALD L- KAPLAN, Primary Examiner 

